The present invention relates generally to medical devices and methods. More specifically, the present invention relates to ultrasound catheter devices and methods for treating occlusive intravascular lesions.
Catheters employing various types of ultrasound transmitting members have been successfully used to ablate or otherwise disrupt obstructions in blood vessels. Specifically, ablation of atherosclerotic plaque or thromboembolic obstructions from peripheral blood vessels such as the femoral arteries has been particularly successful. Various ultrasonic catheter devices have been developed for use in ablating or otherwise removing obstructive material from blood vessels. For example, U.S. Pat. Nos. 5,267,954 and 5,380,274, issued to an inventor of the present invention and hereby incorporated by reference, describe ultrasound catheter devices for removing occlusions. Other examples of ultrasonic ablation devices for removing obstructions from blood vessels include those described in U.S. Pat. Nos. 3,433,226 (Boyd), 3,823,717 (Pohlman, et al.), 4,808,153 (Parisi), 4,936,281 (Stasz), 3,565,062 (Kuris), 4,924,863 (Sterzer), 4,870,953 (Don Michael, et al), and 4,920,954 (Alliger, et al.), as well as other patent publications WO87-05739 (Cooper), WO89-06515 (Bernstein, et al.), WO90-0130 (Sonic Needle Corp.), EP, EP316789 (Don Michael, et al.), DE3,821,836 (Schubert) and DE2438648 (Pohlman). While many ultrasound catheters have been developed, however, improvements are still being pursued.
Typically, an ultrasonic catheter system for ablating occlusive material includes three basic components: an ultrasound generator, an ultrasound transducer, and an ultrasound catheter. The generator converts line power into a high frequency current that is delivered to the transducer. The transducer contains piezoelectric crystals which, when excited by the high frequency current, expand and contract at high frequency. These small, high-frequency expansions (relative to an axis of the transducer and the catheter) are amplified by the transducer horn into vibrational energy. The vibrations are then transmitted from the transducer through the ultrasound catheter via an ultrasound transmission member (or wire) running longitudinally through the catheter. The transmission member transmits the vibrational energy to the distal end of the catheter where the energy is used to ablate or otherwise disrupt a vascular obstruction.
To effectively reach various sites for treatment of intravascular occlusions, ultrasound catheters of the type described above typically have lengths of about 150 cm or longer. To permit the advancement of such ultrasound catheters through small and/or tortuous blood vessels such as the aortic arch, coronary vessels, and peripheral vasculature of the lower extremities, the catheters (and their respective ultrasound transmission wires) must typically be sufficiently small and flexible. Also, due to attenuation of ultrasound energy along the long, thin, ultrasound transmission wire, a sufficient amount of vibrational energy must be applied at the proximal end of the wire to provide a desired amount of energy at the distal end.
A number of ultrasound catheter devices have been described, for example in U.S. patent application Ser. Nos. 10/229,371, 10/345,078, 10/375,903, and 10/410,617, which were previously incorporated by reference. Improvements, however, are always being sought. For example, it continues to be challenging to develop a catheter that is stiff enough to be pushable or “steerable” through vasculature yet flexible enough, at least along part of its length, to navigate small, tortuous blood vessels, such as the coronary arteries or tortuous peripheral vasculature. It is also sometimes difficult to manipulate currently available ultrasound catheter devices, for example to twist or torque the proximal end of the catheter to move the distal end in a way that helps with navigation through the vasculature. Passage of a guidewire through an ultrasound catheter may also be improved upon, such that the guidewire does not interfere with, and may even enhance, disruption of vascular occlusions.
Therefore, a need exists for improved ultrasound catheter devices and methods that provide ablation or disruption of vascular occlusions. Ideally, such ultrasound catheters would have enhanced ability to navigate through small, tortuous blood vessels such as the coronary arteries. It would also be advantageous to have catheters that could be easily manipulated by a user. Ideally, such devices would allow for passage of a guidewire without interfering with, and perhaps even enhancing, disruption of vascular occlusions. At least some of these objectives will be met by the present invention.